The overall aim of this research program isto understand in molecular detail the mechanisms that underlie the replicatton of DNA molecules in prokaryotic and eukaryotic cells. The investigation will be organized along the following lines: 1. Structure of E. coli DNA ligase; a. X-ray crystallographic analysis; b. Determination of nucleotide sequence of DNA ligase gene; 2. RNA primers in the discontinuous replication of the E.coli chromosome and the role of DNA polymerase I in their excision; a. Analysis of Okazake fragments from a mutant deficient in DNA polymerase I and uracil N-glycosidase (E. coli polAex2-ungl); b. The role of DNA polmerase I in the replication of the ColEl plasmid in vitro; 3. DNA replication in Drosophila melanogaster; a. Purification and characterization of DNA polymerase(s); b. Cloning of the DNA polymerase gene; c. Replication of chromatin from Drosophila melanogaster; (1) Identificaion and isolation of replication enzymes and auxiliary proteins; (2) Investigation of the control of DNA replication; d. Identification of DNA polymerase mutants; e. Purification of known replication enzymes (DNA ligase, DNA binding protein, DNA gyrase, etc.) from Drosophila extracts.